Influence of Increasing Prosopis glandulosa on Herbaceous Diversity and Composition on Two Soils in Southern Mixed-Grass Prairie
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We evaluate how increasing cover levels of the tree Prosopis glandulosa Torr. influence herbaceous species richness and composition in two soil-landscape positions in the mixed-grass prairie of the southern Great Plains, U.S.A. Herbaceous species biomass and composition and P. glandulosa cover were monitored on silt-loam bottomlands and clay-loam uplands, in spring, summer, and fall from 1995 to 2001 in 8 paddocks varying in size from 1,283 to 2,130 ha. P. glandulosa trees were closely associated with herbaceous plant composition and richness in different ways on each of the soils. Herbaceous species richness was greater on silt-loam bottoms than clay-loam uplands and decreased little except at the highest P. glandulosa cover levels on both soils. Herbaceous vegetation differed between soil sites and between low (<15%), mid (between 20 and 55%), and high (>60%) P. glandulosa cover levels. The greatest species richness on both soils occurred in areas dominated by herbaceous plants and the least at the highest levels of P. glandulosa cover. On both soils increasing P. glandulosa cover from 0 to 100% was associated with significant declines in herbaceous biomass with C4 tall grasses, C4 mid-grasses, and forbs, small declines with C4 short grasses, and significant increases with C3 annual grasses. Both cool and warm season forb herbaceous functional groups declined with increasing P. glandulosa cover. These results indicate that P. glandulosa reduction on the bottomland sites would yield the greatest benefits in species richness and herbage productivity. 2014 Taylor and Francis Group, LLC.